1. Field of the Invention
The present invention relates to a machine tool having an automatic tool changer for cutting tools.
2. Description of the Prior Art
In a known machine tool with an automatic tool changer, a spindle head in which a tool spindle for removably receiving a tool is carried for rotation about a horizontal axis is vertically movable along an upstanding column mounted on a bed, and a table for mounting a workpiece is provided to face the spindle head with a space. A tool magazine for storing a plurality of small diameter tools which are selectively indexable to a tool removal position is installed at one side of the column in a horizontal direction transverse to the tool spindle. The machine tool is further provided with a tool change unit for changing the tools between the tool magazine and the tool spindle. In the machine tool of this type, it is difficult for the following reasons to store large diameter tools in the tool magazine.
(1) Restraint is imposed on the diameters of tools storable in the tool magazine due to the fact that the pitch of tool sockets which are provided in a side-by-side relation for storage of tools is relatively small.
(2) If the tool sockets horizontally store heavy tools at their tapered receiving bores, the heavy tools may fall off the tool sockets although a mechanism for preventing such tool from falling is usually provided.
Further, the tool change unit uses a tool exchange arm which, when rotated for tool exchange, causes a centrifugal force to act upon each of tools held thereby. Such centrifugal force becomes large in the case of heavy tools and increases the chance of falling of heavy tools.
To preclude these drawbacks, in another known machine tool, a large tool rack for storing a number of large diameter tools is provided on a table, and a tool change operation is effected utilizing feed movements of the table. However, the provision of the large tool rack on the table causes the machine tool to have the following drawbacks.
(1) The working space on the table is diminished.
(2) The number of large diameter tools storable in the rack is limited to only a few.
(3) Cutting chips are scattered to adhere to the stored large diameter tools, which raises a problem in inserting each large diameter tool into the tool spindle.